Heart failure is a major public health problem in the United States, affecting approximately 5 million adults. Despite recent advances in pharmacological therapy and technological devices, heart failure is the most common reason for hospitalization among Medicare patients and is reaching epidemic proportions as the population ages. New and inexpensive interventions that can improve functional capacity, quality of life, as well as delay disease progression, are needed. Tai Chi is a popular mind-body exercise that is a potential adjunctive treatment for heart disease. Tai Chi incorporates both gentle physical activity and meditation. It may be particularly suited to frail and deconditioned patients with heart failure, but has never been rigorously studied in this population. We conducted a feasibility study of Tai Chi in patients with heart failure (n=30) and found that those randomized to a Tai Chi program significantly improved their exercise capacity (six-minute walk distance), quality-of-life (Minnesota Living with Heart Failure score), and neurohormonal status (serum B-type natriuretic peptide levels) compared to patients who did not participate in Tai Chi. In this application, we propose a randomized controlled trial (n=150) over four years that compares a 12-week Tai Chi program with an education attention control. Patients with chronic stable heart failure (systolic dysfunction, left ventricular ejection fraction <40%, New York Heart Association Class I-IV) will be recruited from outpatient primary care and cardiology clinics. Our primary aim will be to examine Tai Chi's effects on functional capacity and quality-of-life. Secondary aims are designed to further elucidate the mechanism of Tai Chi's effects, including examination of cognitive-behavioral or psychosocial influences (e.g., mood, psychosocial functioning, self-efficacy, beliefs and expectations of mind-body medicine) and Heart Failure-specific physiologic/metabolic processes in response to meditative exercise (e.g., neurohormonal status, heart rate variability and markers of autonomic tone, myocardial structure and function). The results of our proposed research will help define the role of Tai Chi in current heart failure management, further our understanding of the mechanism of action, and provide preliminary analyses of the costs and benefits of treatment.